Exposure apparatuses for semiconductor processing are commonly used to transfer images from a reticle onto a semiconductor wafer during semiconductor processing. A typical exposure apparatus includes an illumination source, a reticle stage assembly that holds and positions a reticle, an optical assembly, and a wafer stage assembly that holds and positions a semiconductor wafer.
Recently, extreme ultraviolet lithography (“EUVL”) systems that use an extreme ultraviolet illumination source have been proposed to increase the number of transistors transferred to the wafer. The extreme ultraviolet light must travel in a vacuum to avoid the absorption of the extreme ultraviolet light.
The reticle in these systems is a reflective type and requires the use of an electrostatic chuck to both support the reticle, and flatten any unevenness in the reticle. Further, any particles positioned between the reticle and the chuck can cause additional unevenness in the chucked reticle. Current EUVL standards specify that the chucked reticle has a surface flatness not to exceed less than fifty nanometers peak-to-valley.
Unfortunately, existing electrostatic chucks may not generate sufficient force to sufficiently flatten particles occurring between the reticle and the chuck.